Three-bestseller pesticides in Brazil: Freshwater concentrations and potential environmental risks

Agricultural production in Brazil is favored by weather conditions and by the large amount of available land. Therefore, currently, Brazil is the second largest exporter of agricultural products globally. Pesticides are widely used in Brazilian crops due to their high efficiency, their low cost, and permissive legislation. However, pesticides tend to reach water resources threatening organisms and the water quality. Thereby, we aimed to review the surface freshwater concentrations of the three-bestseller pesticides in Brazil (glyphosate, 2,4D, and atrazine), and discuss the results with sales, legislation, toxicity and potential risks. For that, we performed a systematic review of quantitative studies of glyphosate, atrazine, and 2,4D in Brazilian freshwater and included monitoring data provided by the Brazilian Ministry of Health in our analysis. Finally, we calculated the risk assessment for the three pesticides. Only a few scientific studies reported concentrations of either of the three-bestseller pesticides in Brazilian freshwaters. Between 2009 and 2018, an increase in the sales of 2,4D, atrazine, and glyphosate was observed. It was not possible to evaluate the relation between concentrations and sales, due to limited number of studies, lack of standard criteria for sampling, individual environmental properties, and type of pesticide. Atrazine showed a higher toxicity compared to 2,4D and glyphosate. Regarding the environmental risks, 65%, 72%, and 94% of the Brazilian states had a medium to high risk to 2,4D, atrazine, and glyphosate, respectively. Finally, 80% of the Brazilian states evaluated showed a high environmental risk considering a mixture of the three pesticides. Although most of the environmental concentrations registered were below the allowed limits according to the Brazilian legislation, they are already enough to pose a high risk for the aquatic ecosystems. We, therefore, strongly recommend a revaluation of the maximum allowed values in the national surface freshwater Brazilian legislation.